The present invention relates to apparatus of the type used in embossing or similarly deforming lengths of web material such as paper or the like and to methods for producing an embossing surface in the embossing apparatus. More particularly, the invention pertains to improvements in embossing rollers which receive lengths of web material therebetween in such a manner that the web material is embossed as it passes through the rollers.
The prior art apparatus used for embossing and intended to apply a continuous embossing pattern to a web generally comprised at least a pair of opposed embossing rollers which have an embossed pattern etched or machined directly into the surface of at least one roller. Rollers of this type are advantageous in that they can impart a continuous embossing pattern to the web without breaks or interruptions. However, rollers of this type have proved to have a variety of disadvantages which make them unduly expensive to manufacture and to maintain in operation. For example, either as a result of continued use or as the result of foreign materials passing through the rollers, the embossing patterns on the rollers often become worn or damaged. In order to regrind, remachine or otherwise repair the embossing pattern, it is necessary to remove the entire roller or rollers from the embossing machine. The removal process itself causes the embossing machine to be out of operation for sometime and is thus costly and the actual process of repairing the embossing pattern on the surface of the rollers is also expensive. Because wear and damage to the rollers is somewhat prevalent, it is also generally necessary to maintain at least one extra pair of rollers on hand to minimize down time during repair. Furthermore, when the embossing patterns have been worn to the point where there is no longer enough of the roller surface material remaining to permit further regrinding or remachining or when there has been major damage to the rollers, it is generally necessary to either replace or to completely rebuild the roller and replace or recut the roller gears. Another drawback to the prior art embossing rollers is that in many cases one particular area will wear at a much greater rate than the remainder of the embossing surface. Due to economic considerations, the rollers are frequently used despite this wear and until the entire surface of the rollers have been sufficiently worn to warrant regrinding or replacement. Until regrinding or replacement is feasible, the worn area of the rollers will produce an embossing pattern of inferior quality.
An additional drawback of the prior art rollers is that, in the event it is desired to change the embossing pattern applied to the web, it is necessary to remove the patterned rollers from the machine. As previously stated, the process of exchanging rollers is often unduly time consuming and costly.
It is known to use means such as magnetic cylinders to support independent or separate printing plates or die cutting plates. The following U.S. patents, for example, disclose magnetic cylinders used for printing and magnetic printing plates for use therewith: U.S. Pat. Nos. 3,721,189; 3,885,498; 3,824,927; 3,882,775; 3,885,497; 3,820,460; 3,670,647; and 3,837,959. However, it should be realized that printing and embossing differ both as regards the equipment employed and the nature of the process. For example, printing involves laying ink on the surface of a web by means of a printing roll, with the web being supported by a back-up roll or the like, and no physical deformation of the web is carried out. However, in embossing it is necessary to physically deform the web passing between a pair of embossing rollers which have projections which interengage and, as a result, the embossing roll surfaces are subjected to physical forces not involved in printing processes. Due to the problems inherent in embossing such as the higher pressures which must be applied by embossing rollers to a web, no satisfactory means have previously been developed for magnetically mounting an embossing plate on a supporting cylinder or for producing a suitable removable embossing plate or for effecting accurate alignment of such embossing plates prior to and during the embossing operation.